A target placed at a survey point has been required to be collimated, in order to measure the position of the survey point or the like by means of a surveying instrument such as a conventional total station (electronic distance/angle meter) In recent years, in order to lighten labor required to collimate a target and in order to reduce collimation errors produced by habits of an operator, a surveying instrument provided with an automatic collimation device has appeared on the market The automatic collimation device is structured to emit collimation light along a collimation axis (optical axis) of a telescope of a surveying instrument, then calculate the direction of a target by receiving collimation light reflected from the target, and automatically direct the telescope toward the target. The surveying instrument provided with the thus structured automatic collimation device has come to include a remote controller so that a survey can be performed even by a single operator from a place apart from the main body of the surveying instrument.
However, if the surveying instrument provided with the automatic collimation device is operated under a command issued from the remote controller during a survey, a scanning operation must be performed with the telescope in a wide range in order to catch the target within the narrow visual field of the telescope. Therefore, disadvantageously, much time is consumed for automatic collimation, and the survey cannot be smoothly performed.
To solve this problem, a surveying instrument disclosed in Japanese Patent No. 3075384 is known. The surveying instrument disclosed in this document is shown in FIG. 6 and FIG. 7.
In the surveying instrument 11, light receiving units 25 and 26 for receiving signal light from the remote controller 27 are provided on the front and the back thereof, respectively. This signal light functions also as guide light used to show the position of the remote controller 27′. Each of the light receiving units 25 and 26 is shaped like a pyramid, and has four light receiving surfaces A, B, C, and D as shown in FIG. 7.
When an operator in the vicinity of a reflecting prism (e.g, corner-cube prism) 23 directs the remote controller 27 toward the surveying instrument, signal light emitted from the remote controller 27 strikes the light receiving unit 25. If the vertex T of the light receiving unit 25 faces the remote controller 27, the four light receiving surfaces A, B, C, and D become identical with each other in the amount of incident light of the signal light. However, if the vertex T of the light receiving unit 25 does not face the remote controller 27, the four light receiving surfaces A, B, C, and D do not become identical with each other in the amount of incident light of the signal light. Therefore, the direction of the remote controller 27 is calculated by comparing outputs emitted from the four light receiving surfaces A, B, C, and D by use of a control means not shown, and the telescope 12 is turned toward the remote controller 27. When the collimation axis O of the telescope 12 is directed toward the remote controller 27, i.e., toward the reflecting prism 23, an LED 31 mounted on the front of the surveying instrument 11 is lit, and the operator is informed of this. Hereafter, the telescope 12 automatically collimates the direction of the reflecting prism 23 by means of an automatic collimation device not shown.
In this surveying instrument, the direction of the reflecting prism 23 is swiftly found by the light receiving units 25 and 26 prior to automatic collimation. Therefore the reflecting prism 23 does not need to be searched while performing a scanning operation of a wide range with the telescope 12 having a narrow visual field, and hence time taken until the collimation completion of the reflecting prism 23 is shortened, and the survey can be smoothly performed.